1. Field of the Invention:
The present invention relates to a device for converting a video data with a particular scan rate supplied from a radar receiver or other sources to a video data with a different scan rate.
2. Description of the Prior Art:
A digital scan converter receives a slow scan rate video data available from a radar receiver and converts it to a high scan rate video data and displays the resultant video data on a television or an orthogonal display. A prior example of a digital scan converter is disclosed in U.S. Pat. No. 3,765,018.
FIG. 1 is a block diagram illustrating an examplary arrangement of a prior digital scan converter. As shown in the figure, an analog input video signal from an input terminal T1 is converted to a digital signal by an analog-to-digital converter 1 (hereinafter simply referred to as A/D converter), and stored temporarily in an input buffer 2. An azimuth data from an input terminal T2 is converted in a write address generator 5 to X-Y coordinates, and transferred to a X-Y coordinate random access memory 3 via an address switching circuit 6. The video signal temporarily stored in an input buffer 2 is read out synchronized with an address data from the write address generator 5, transferred to the random access memory 3, and stored in the address. For the video signals stored in the memory 3, read scanning address data prepared in an output counter 7 is supplied to the memory 3 via the address switching circuit 6, and the video signal corresponding to the read scanning address data is read out of the memory 3 in succession in conformity with prescribed read scanning. The read video signal is converted to a digital signal through a D/A converter 4, and delivered to an output terminal T.sub.3. Thus, with the input video signal scanned in polar coordinates (R,.theta.), the signal is converted to a read scan specified by the output counter 7 (for example, a rectangular coordinate (X, Y) scan).
As described above, in the prior digital scan converter, the video signal thus scanned and converted is read out only from a region of one kind of the memory 3 (the whole region of the memory 3, in typical). Accordingly, for the prior video signal, only a picture image present in the region of one kind is displayed on a display (for example, on a TV display). In a harbor radar system, etc., picture images available from one radar or picture images from a plurality of radars may be synthesized into one system, and scan-converted and displayed simultaneously on a plurality of displays for every different regions. For this reason, in such a case, scan converters corresponding to the displays in the number thereof are required from the above described reason.